Electric range surface heating unit



P 1, 1954 e. R. RADLEY 2,689,903

ELECTRIC RANGE SURFACE HEATING UNIT Filed June 3, 1950 2 Sheets-Sheet 1 Patented Sept. 21, 1954 ELECTRIC RANGE SURFACE HEATING UNIT Guy It. Radley, Whitefish Bay, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application June 3, 1950, Serial No. 166,033

This invention relates to improvements in electric range surface heating units.

An object of this invention is to provide an electric range surface heating unit which is of improved construction and is easy and economical to manufacture.

Another object is to provide an electric range surface heating unit which protects against boilover of liquids.

Another object is to provide an electric range surface heating unit which provides for easy re- 3 Claims. (Cl. 21937) placement of the reflecting material below the heating elements.

Another object is to provide an electric range surface heating unit having improved means for providing good thermal contact between the heater elements and the bottom of a vessel placed upon them even though the bottom of the vessel be not truly flat.

Other objects and advantages will hereinafter appear.

In the accompanying drawings which illustrate an embodiment of my invention,

Figure 1 is a top plan view of an electric range surface heating unit incorporating the features of my invention;

Fig. 2 is a vertical sectional view taken along the line 2--2, as shown in Fig. 1, and

Fig. 3 is a schematic and diagrammatic representation illustrating my system for preventing boil-over.

In Figs. 1 and 2 the heating unit is shown as having an outer circular rim member H) which is made of stainless steel or other metal. At the lower end of said rim member there is an inwardly turned flange II on which is supported a circular disc l2 which is made of a relatively strong insulating material such as Transite.

Circular heater elements I3, l3", 13 are supported in a manner hereinafter to be described on a spider assembly which consists of a central tubular metal member to which are attached by welding or other means U-shaped supporting arms 26 26 26, 26 26 The spider assembly is easily removed from the unit housing simply by lifting, and when in place it is supported by the insulating bottom disc H.

In order to insure good thermal contact between the heater elements and the bottoms of vessels which may be placed upon them, I mount the heater elements upon the spider arms in the following manner. Clips are attached to the outer metal sheath of the heater elements by welding or other means. Depending from clips 30 are studs 3| which are positioned to be inserted in holes 32 in U-shaped spider arms 26 to 26. To prevent undue movement of the heater element terminals M in the terminal clips H, the holes 32 in spider arms .26 and W have very small clearance for the studs 3| while the holes 32 in arms 26 26 and 26 have large clearance for the studs. This allows for expansion and contraction of the heater units. As best shown in Fig. 2, heater element W is fixed against vertical displacement on spider arm 26 by means of bushings 33 and spring clip 34 which cooperates with stud 3|. Similar mounting of heater element 13 is made on spider arms 26*, 2 6 26 and 26*.

However, heater elements I3 and 13 are not fixed against vertical displacement. They are normally urged to a level above that of heater element I3 by stainless steel helical springs 20 which are positioned between the depending sides of U-shaped spider arms 26 to 26 and thus are shielded from the radiant heat of the heater elements. Springs 20 are mounted horizontally with one end 2| projecting through a punched hole 22 in one side of the spider arm and the other end '23 projecting through an opening in the stud 3!. In this manner heater element I3 is mounted on each of spider arms 25* to 26 and in the same manner heater element I3 is mounted on spider arms 26, 26 and 26 Upward movement of heater elements 13 and 13 is limited by the engagement of spring ends 23 with the underside of spider arms 26 to 26 Downward movement of heater elements I B and 13 may be limited by the engagement of clips 30 with the upper surface of the spider arms, or preferably, by the engagement of the lower ends of studs 3| with the upper surface of insulating disc it. Thus it will be seen that if a vessel having a substantially flat bottom is placed upon the heating unit, the upper faces of the heater elements I3 to 13 will lie along a plane as indicated in Fig. 2 by dotted line at. However, more commonly the vessel bottom is deformed in one direction or the other. If the vessel bottom is convexly shaped, the heater elements 13 to l3 will assume a position as indicated by dotted line y and will continue to make line contact with the bottom of the vessel. Similarly, if the vessel bottom is concavely shaped, the heater elements will lie along a plane as indicated by dotted line 2. Warping of the heater elements W to [33 is also reduced to a minimum by making the ratio of width to length greater than unity. The pre-- ferred ratio will vary between 1:12 and 1:2. As

will be obvious, reduction in warping will further assist in maintaining line contact between the vessel and the heater elements. Thus, it will be seen that my improved electric range surface heating unit assures suflicient heat conduction regardless of the shape of the vessel bottom which is placed upon it.

Another important feature of my invention is the provision for ready removal and replacement of the heater elements. The heater elements are substantially circular in shape and have depending end terminals M which are inserted through openings [5 in the terminal box 16 which is formed of insulating material. Inside the terminal box the terminals l4, which are preferably made of nickel, engage with their respective stainless steel spring terminal clips I1. Terminal bolts l8 hold clips I! in position and pass through insulating disc I2 for connection with conductors (not shown). It should be noted that the clips H havegripping' edges lilywhich edges serve to break through any scale which may form on the terminals."

Thus, it will'be'seen'that my improved electric range surface'hea'ting unit permitsready removal of the heatereleriients l3 to I3 additional advantage in'that' it also permits easy cleaningo'f the unit withouttlie necessity of tipping the entire unit up cut of its mounting in the stove, apracticefwhich if done too often tends to' weaken'andbreak the conductors connected to the unit terminals. As an additional aid to the easy cleaning of theunit and also to assist inthe reflection of radiant heat, I prefer to cover the insulating base or disc l2 with a circular sheet 28 of aluniinumfoil'or other similar material; the sheet having portions cut outso that-the terminal box l6 and the tubular member 25 will project therethrough. Should-the foilsheet 28 become soiled, it is then'a simple matter to remove the heater elements" and their supporting spider assemblyand replace the sheet with afresh one.

Another very important feature ofmy improved electricrangesurface heating unit is the provision of novelmeans for providing quick-heat while protecting against boilover. In Fig 3 I have shown the heater elements I3 to l3 and associated switching means indicated generally by numeral' ill. It will be seen that the switch means provides seven different degrees of heat by rotation'of the cam members 4| tocommutate the various circuits. However, in addition to the usual sevenpositions of the switch, designated by the numerals 1- through 7, and the off position, I have provided another position designated Auto." In this position heater elements 13, [3 and I3 are connected for energization across lines 1. and L Element I3 is energized. by a circuit which leadsfrom line L through closed contacts 42, through heater element l3, and thence through closedcontacts 43 to line L Heater elements 13 and 13' are energized by a circuit which leads from line L through contacts 5| of control member SIL-through closed contacts M, thence through elements I3 and 13 and closed contacts 43 to line L The combined wattage of heater elements [3 l3 and 13 is sufficient to rapidly bring liquids placed upon the unitto their boiling point. However, when controlmember 50 operatesto open contacts 5P the circuit through heater elements 13 and [3 is opened. This leaves only heater element 13 energized, anditswattage value is only suiiicient to maintaina moderate heat; Under normal con ditions, because of the time lag of the control member, the unit will remain at this heat until the user returns to reset the switch to whichever setting is desired for continued heating.

I will now describe the construction and operation of control member 50 in detail. Referring to Fig. 1 and more particularly to Fig. 2, control member 50 is shown as having a metal cartridgelike housing 52 which is positioned for vertical movement within tubular member 25. A compression spring 53 is positioned between the supporting base I: and the lower end of housing 52 and serves to normally urge said housing to the position shown in Fig. 2. Within housing 52 is an insulating disc 54' on which are positioned a pair of stationary terminal members 55 having contact portions 5|. A compression spring 58 is positioned between insulating disc 54 and a bridging contact member 51, normally urging contact portions 5l which are mounted on member 51 into engagement with stationary contacts 5|. Above the contacts 5| is ametal protecting shield 58 which is peripherally welded or otherwise secured to the inner wall of housing 52. Shield 58 is centrally apertured to receive an actuatingrod 59 the lower end of which abuts against bridgcontact member 51'. Downward movementof rod 59 serves to open contacts 5F and is effected by means of a bimetallic member 60.

Bimetallic member 60 is retained within a peripheral groove 6| formed near the upper end In'this manner goodthermalc'ontact is assured between it and the" bottom of avessel placed upon the unit. Also, thecontrol member, similarrto heater elements I 3* and I 3, is depressed to a posi tion determined by the configuration'oi the vessel bottom. In this manner-,yreliable and accurate calibration of the bimetallic member 60 is assured.

The operation of the control member is as follows. With the vessel containing the liquid to be heated placed on the surface heating unit, switch as is placed in the position indicated by Autof whereupon current flows through heater elements I3, l3 and I3. In series with the circuit through heater elements l3' 'and I3 are the contacts 5| which are connected incircuit by the conductors 55 and 55 which are led through the lower end of housing 52 and through supporting base l2. The temperature of the bimetallic member 60, which is in direct contact with the vesselbottom, increases with that of the liquid contained there- At a temperature dependent upon its calibration, preferably between C. and C'., the bimetallic, member straps to present a concave surface. In so doing, it depresses the actuating rod 59 which in turn forces open contacts 5| against the bias of spring 5'3. Thereupon, current no longer flows through heater elements I3 and I3. Since the heating capacity of element It) is insufficient to bring the liquid on up to its boil ing point, boil-over of the liquid is thuseffectively prevented.

It should also be notedthat when the control member 50 is in its open or tripped condition, bimetallic member fio will nolonger be in contact with the vessel bottom. Instead, the vessel will rest upon housing edge 62''. This is an important feature because'it helps to preserve the calibretion of the bimetallic member 60 which would otherwise be affected by the high temperatures irivolved in frying, broiling, etc. Thus tubular nous ing 52, in addition to providing supporting means for the bimetallic disc 60, also efiectively protects it against the deleterious effects of excessive heat.

I claim:

1. An electric range surface heating unit comprising a heat insulating base member, a heater element supporting spider assembly supported by said base member, said spider assembly including downwardly turned U-shaped supporting arms formed of an oxidation resistant metal, three circular heating elements for concentric mounting upon said supporting arms, means fixedly mounting the middle of said heating elements to said supporting arms, and means resiliently mounting the inner and outer heater elements upon said supporting arms, said last mentioned means comprising studs depending downwardly from said inner and outer elements for projection through openings in the upper face of said supporting arms, and stainless steel helical springs horizontally mounted between the sides of said supporting arms adjacent said openings with one end operably connected to their respective studs, whereby said elements may move relatively to and independently of each other to insure a shape-conforming engagement with the bottom of a vessel placed on said unit and the springs permitting such movement are shielded from the radiant heat emitted by said elements.

2. An electric range surface heating unit comprising a housing having a heat insulating disc shaped base retained within a circular metal rim, a spider assembly supported by said base and having an open central tubular supporting member with inverted U-shaped stainless steel supporting arms extending radially therefrom, a middle circular heating element fixedly mounted on said supporting arms, inner and outer circular heating elements having downwardly depending studs projecting through openings in the upper face of said supporting arms, stainless steel helical springs horizontally mounted within said supporting arms adjacent said openings and having one end thereof operably connected to their respective studs for resiliently urging said latter heating elements to a position above that of said middle element whereby said elements may be moved relatively to and independently of each other and to said middle element to insure a shape-conforming engagement with the bottom of a vessel placed on said unit, a control member for at least one of said heating elements contained within a tubular housing positioned for axial movement within said central tubular supporting member, a bimetallic normal- 1y convex actuating disc positioned at the upper end of said control member housing for normal engagement with, said vessel bottom, means formed integrally with the upper end of said control member housing for separating said vessel bottom and said disc when the latter has snapped into a concave shape under the influence of a preselected degree of heat, and means positioned between said base and said control member housing for resiliently urging the latter into engagement with said vessel bottom.

3. The combination with an electric range sur face heating unit comprising a plurality of heating elements for heating of a vessel positioned thereon, of a tubular metal housing resiliently mounted relative to said heating elements to urge the upper end of said housing above said heating elements, a disc-shaped electrical insulating member positioned at one end of said housing, a pair of stationary contacts fixed to said disc within said housing, and in circuit with at least one of said heating elements, a bridging contact member normally resiliently urged into engagement with said stationary contacts by a compres sion spring positioned between said contact member and said insulating disc, a dish-shaped bimetallic disc retained within a peripheral groove formed in the upper end of said housing so that its normally convex side will project in an axial direction beyond the end of said tube for surface contact with vessels positioned on said heating elements, an inwardly turned portion at the same end of said housing for retaining said bimetallic disc in said groove and for protecting said disc when the surface with which said control member is in contact is at a temperature higher than its actuating temperature by preventing surface contact between the vessel and said disc while the normally convex side of the latter is concave, and an axially movable actuating rod positioned between said disc and said bridging contact member for moving said latter member out of engagement with said stationary contacts upon actuation of said disc References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,207,462 Kurtz July 9, 1940 2,207,634 Myers et a1. July 9, 1940 2,261,533 Vineberg Nov. 4, 1941 2,262,026 Hastings Nov. 11, 1941 2,263,350 Challet Nov. 18, 1941 2,270,293 Grunder Jan. 20, 1942 2,272,658 Challet Feb. 10, 1942 2,288,967 Challet July 7, 1942 2,311,371 Crowley Feb. 16, 1943 2,399,423 Bletz Apr. 30, 1946 2,409,414 Bletz Oct. 15, 1946 2,410,013 Clark Oct. 29, 1946 2,419,083 Myers Apr. 15, 1947 2,427,944 Clark Sept. 23, 1947 2,430,715 Grayson Nov. 11, 1947 2,534,097 Akeley Dec. 12, 1950 2,632,436 Williams Mar. 24, 1953 

